CVD apparatus is conventionally used to form various thin films in a semiconductor integrated circuit. Such CVD apparatus can form thin films such as SiO.sub.2, Si.sub.3 N.sub.4, Si or the like with high purity and high quality. In the reaction process of forming a thin film, a reaction vessel in which semiconductor substrates are arranged can be heated to a high temperature condition of 500.degree. to 1000.degree. C. Raw material to be deposited can be supplied through the vessel in the form of gaseous constituents so that gaseous molecules are thermally disassociated and combined in the gas and on the surface of the specimen so as to form a thin film.
A plasma enhanced CVD apparatus utilizes a plasma reaction to create a reaction similar to that of the above-described CVD apparatus but at a relatively low temperature in order to form a thin film. The plasma CVD apparatus includes a specimen chamber, a gas introduction system, and an exhaust system. For example, a plasma enhanced CVD apparatus is disclosed in U.S. Pat. No. 4,401,504. Plasma is generated in such an apparatus by microwave discharge through electron-cyclotron resonance (ECR). A specimen table is provided in the specimen chamber, and plasma generated in the plasma formation chamber passes through a plasma extracting orifice so as to form a plasma stream in the specimen chamber. The specimen table may have a cooling mechanism in order to prevent a rise in temperature of the specimen due to the plasma action.
During electron-cyclotron resonance chemical vapor deposition of SiO.sub.2, extraneous SiO.sub.x film deposits on various surfaces throughout the reaction chamber. As these deposits become thicker, they begin to crack, flake and spall, thus generating particles within the reaction chamber that contaminate wafers processed in the reactor.
U.S. Pat. No. 5,200,232 discloses a reaction chamber designed to minimize particle generation in a plasma enhanced chemical vapor deposition reactor, the disclosure of which is incorporated herein by reference. Specifically, all surfaces near or within a line-of-sight path to the wafer are replaced with, or shielded by, particle control surfaces. These surfaces are temperature controlled to prevent thermal cycling from occurring in the extraneous deposits, since thermal expansion and contraction produces mechanical stresses that result in cracking and delamination, thus generating particles. The surfaces are also designed so that no sharp edges or comers occur which might concentrate mechanical stresses, and thus act as a catalyst for particle generation. Also, in the case of SiO.sub.2 deposition, the particle control surface is constructed out of aluminum, to which extraneous SiO.sub.x adheres very well. This combination of temperature and adherence control effectively eliminates particle generation, at least until the extraneous film becomes so thick that intrinsic material stresses overcome the adhesion strength, and particle generation begins to occur.
In conventional systems, when particle generation begins, the particle control surfaces must be removed and replaced with new or cleaned parts. The cleaning process typically involves a carbide bead-blasting procedure, or machining with a lathe. The regular removal of particle control hardware is undesirable for several reasons. Most importantly, the reaction chamber must be opened to the atmosphere and subjected to human handling and mechanical operations. This invariably results in significant particle contamination. Furthermore, each hardware change requires trained technicians to perform the change, and to ensure compliance with cleanliness and safety regulations. In addition, the trained technicians must requalify the safety and functioning of the tool. This is both an expensive and a time-consuming process. Furthermore, the downtime required for the change adversely affects the tool throughput, which increases production costs. Additional costs result from the fact that the particle control hardware is a consumable item and several sets must be available to be cycled through after the cleaning steps. Finally, any mechanical cleaning will eventually wear out the parts, thus necessitating regular replacement. Thus, there exists a need in the art for improving the methods for removing extraneous film buildup on surfaces in the reaction chamber, especially line-of-sight surfaces and specimen surrounding surfaces. The term "line-of-sight surfaces" as used herein means surfaces from which a straight line can be drawn directly to a specimen mounted in the reaction chamber. The term "specimen surrounding surfaces" as used herein means surfaces surrounding the specimen mounted in the reaction chamber and which are directly contacted by a plasma stream. The term "specimen" as used herein means any semiconductor substrate, such as a wafer of silicon or other material, having a fiat or uneven surfaces onto which a film is formed by a plasma reaction.
It is known in the art to use a magnetron plasma device for deposition/etching of a target or samples on the target, as disclosed in U.S. Pat. No. 4,588,490. Also, use of a magnetron plasma to clean interior surfaces of a chamber is disclosed in U.S. Pat. No. 4,434,038.